I am using a trigger to change the APP_STATUS to "TO_DO" after I create a new case via a REST call. I noticed in the APPLICATION table a column, APP_STATUS_ID. It looks like APP_STATUS_ID contains a '1' when the status is DRAFT and a '2' when the status is TO_DO. Is this correct? Where is APP_STATUS_ID used?
But my big question is why does the change status trigger also change the APP_STATUS_ID?

OK thanks. That is what I thought. You will need to update your documentation where you talk about creating a case via REST. The change status php code only changes the APP_STATUS, it should probably also change the APP_STATUS_ID as well.